Each year approximately 400,000 rotator cuff surgeries are performed in the United States. While operative techniques have improved, the failure rate remains unacceptably high (30-35%). A recognized risk factor for surgical failure is fatty muscle infiltration. The muscles of the rotator cuff undergo progressive fatty infiltration following tendon tear. While surgical techniques have been developed to address torn rotator cuff tendons (sutures and suture anchors), there are currently no effective methods to reverse fatty infiltration. We suggest that intramuscular delivery of muscle matrix gel will stimulate myogenesis and reverse fatty muscle infiltration. To determine the efficacy of this premise our team will develop next generation matrix gels using human muscle (aim 1), test gel performance in a fatty infiltration shoulder cuff model (aim 2), and explore matrix triggered mechanisms of wound healing (aim 3).